1. Field of the Invention
This invention relates generally to the field of access doors providing access to the interior of a duct, and specifically to an access door designed to provide easy access to the interior of grease ducts and other ducts serving, for example, commercial and institutional kitchens, allowing the cleaning, servicing, and inspection of the ducts, or any wires, equipment, or other components located within the ductwork.
2. Prior Art
Access doors for ductwork are well known in the prior art. Historically, access doors formed from two plates with a gasket between the plates have been known. The access doors are bolted together so that the two plates may be separated in distance and then the inner plate is inserted into the duct through the duct opening. The outer plate and the gasket remain outside the duct and, when the bolts are tightened, the two plates are drawn together to seal the opening in the duct. This generic type of duct access door has become known as a xe2x80x9csandwichxe2x80x9d door for obvious reasons.
To enter the sheet metal ductwork, access openings are usually cut in a rectangular shape which permits the inner plate of a xe2x80x9csandwichxe2x80x9d access door to be maneuvered through the diagonal of the rectangular opening and to be positioned inside the duct.
As ducts have come to be used in kitchen service to remove vapors and grease from cooking areas, duct access doors have become more sophisticated in order to obtain approval by Underwriters Laboratories for use in an environment where grease and cooking vapors are present since a fire may occur inside the duct under such conditions. Access doors approved by Underwriters Laboratories must completely seal the duct in order to obtain such approval.
One type of access door which has obtained Underwriters"" approval is described in U.S. Pat. No. 5,165,189 issued Nov. 24, 1992 to Bernard P. Besal. This access door requires a frame that must be retrofitted into the duct opening in order to receive a cover with a gasket. This retrofitting is time consuming and expensive and requires a multiplicity of fasteners in order to obtain the necessary sealing.
Historically, the sandwich-type access doors have not been able to meet the sealing requirements of the Underwriters Laboratories for use with grease ducts serving, for example, commercial and institutional kitchens. The present invention provides a sandwich-type access door which meets the Underwriters Laboratories"" requirements and has been approved by Underwriters Laboratories.
An access door to allow access to the interior of a duct having a rectangular opening formed in the duct is provided. The access door includes first and second rectangular plates which are larger in both dimensions than the rectangular duct opening. The first rectangular plate has at least two bolts fixed to it that project outwardly from the first rectangular plate and the first rectangular plate also has at least four threaded apertures at the corners of the plate to receive bolts. The second rectangular plate which is of the same size as the first plate has holes registering with the bolts fixed to the first plate and with the threaded apertures at the corners of the first plate. A non-flammable gasket which can withstand temperatures resulting from burning debris located within a duct is fixed to the second plate and positioned between the first and second plates and is coextensive with the plates. Nuts are threaded onto the two bolts fixed to the first plate. Bolts extending through the holes in the second plate and threaded into the threaded apertures are provided. The nuts and bolts are unthreaded sufficiently to permit the first plate to be inserted into the duct and thereafter the nuts and bolts are tightened to draw the first and second plates together and to exert a compressive force upon the gasket.
The access door of the present invention can be inserted into any duct rectangular opening without modification of the rectangular opening in any way whatsoever. The usual procedure is to provide an access opening template with the access door of the present invention so that the template fixes the size of the rectangular duct opening and provides a rectangular opening which is two inches less on each side than the dimension of the access door so that when the access door is positioned within the duct, there is a one inch space where the access door overlaps each side of the rectangular opening.
By strategically positioning additional bolts at the four corners of the access door, the access door has been made air tight, vapor tight, and grease tight so that Underwriters Laboratories"" approval has been obtained for the access door of the present invention.
Accordingly, it is an object of the present invention to provide an access door for ductwork which remains structurally intact and leak-proof under duct fire conditions.
It is another object of the present invention to provide an access door which provides easy access to the interior of ductwork.
Another object of the present invention is to provide a sandwich-type duct access door approved by Underwriters Laboratories for use with various ducting systems.
These and other objects of the present invention all become readily apparent as this description proceeds in conjunction with the accompanying drawings.